WBCs fight against infections.
RBC
White blood cell, also called leukocyte or white blood corpuscle, has a nucleus, is capable of motility, and defends the body against infection and disease by ingesting foreign materials and cellular wastes, by destroying infectious agents and cancer cells, or by producing antibodies.
When you get sick, your white blood cell count is higher than normal. This is because your body is releasing more of these cells to fight the infection.